1. Field of the Invention
The present invention relates to a lubricating oil supplying structure for a crankshaft, and in particular to a lubricating oil supplying structure for a crankshaft, which is provided to a connecting rod and which can smoothly supply a lubricating oil to a connecting rod bearing contacting a crank pin.
2. Description of the Related Art
In general, as shown in FIGS. 6 and 7, a crankshaft 51 of, for instance, a straight four cylinder engine 50 is supported and fixed within a crank case 53 by a crank journal support structure 55. The crank journal support structure 55 is constructed such that a plurality of crank journal bearings 67 of semi-circular shape in a aide view are provided at lower end portions of plural crank journal supporting wall portions 66 within the crank case 53 of a cylinder block 52, and the crank journal bearing 67 are coupled respectively to bearing caps 56 of semi-circular shape in a cross view.
On the other hand, as shown in FIGS. 7 and 8, a piston 59 is axially supported through a piston pin 68 by a small end side 58 of the connecting rod 57, and a big end side 60 of the connecting rod 57 is axially supported through a connecting rod bearing 62 by a crank pin 61 of the crankshaft 51.
The crankshaft 51 is provided with a lubricating oil supplying passage inside thereof unillustrated, and a lubricating oil pressured by an oil pump is supplied to a crank journal bearing 67 contacting the crank journal 54 and the connecting rod bearing 62 supporting the connecting rod 57 to the crank pin 61, thereby lubricating the crank journal 54 and the crank journal bearing 67, as well as the crank pin 61 and the connecting rod bearing 62.
That is, the crank journal bearing 67 is provided with an oil groove (not shown), to which the lubricating oil pressured by the oil pump is supplied. The lubricating oil spread out from the oil groove lubricates between the crank journal 54 and the crank journal bearing 67. The lubricating oil supplying passage is provided between the crank journal 54 and the crank pin 61, one end of which is opened to an oil groove of the crank journal bearing 55, and the other end of which is opened at a surface portion of the crank pin 61 to a slidingly contacting surface 63 of the connecting rod bearing 62 with the crank pin 61 to which the connecting rod 57 is mounted.
Therefore, the lubricating oil entering the oil groove provided in the crank journal bearing 67 by the action of the oil pump lubricates the inner circumferential surface 65 of the crank journal bearing 67. The lubricating oil also reaches the crank pin 61 through the lubricating oil passage from the oil groove, and spread to the slidingly contacting surface 63 of the connecting rod bearing 62 to lubricate the slidingly contacting surface 63 of the connecting rod bearing 62 with the crank pin 61.
Besides, a combustion load within the cylinder acts the most largest in a cylinder axial direction to the crank journal bearing 67 through the piston 59 and the connecting rod 57. That is, the generated combustion load acts the most largely to the bearing cap 56 located at the lower and portion of the bearing as shown in FIG. 6.
In this case, for example, if the oil groove is provided in the bearing inner circumferential surface 65 at the bearing cap 56, the pressure receiving surface of the bearing inner circumferential surface 65 where the combustion load acts is reduced by the provision of the oil groove. Consequently, the combustion load against which the crank journal bearing 67 can bear is made small, requiring an upper limitation to the generated combustion load.
Therefore, in designing an engine, in general, a required engine power is first determined, and then a combustion pressure necessary for the engine power and an engine revolution speed are calculated, and a bearing width necessary for the combustion pressure is determined. In this case, as mentioned above, if it is necessary to inevitably provide an oil groove in a portion receiving the combustion load, the bearing width dimension in that portion must be made large. Consequently, the bearing width is increased, and the engine weight is enlarged correspondingly. This is disadvantageous in designing the engine, for inviting the increases of the bearing width and the engine weight.
For this reason, conventionally, an oil groove is normally provided in the crank journal bearing 67 not over the entire circumference of the bearings and which is located at a portion where the generated combustion load does not act directly. For example, in the case where a cylinder arrangement of an engine is straight or V-type, the oil groove is typically provided partially in the crank journal bearing 67 of the crank case to avoid such an instance that it is provided in the crank journal bearing 67 of the bearing cap 56.
When the oil groove is provided in the entire circumference of the crank journal bearing 67, the lubricating oil supplying passage is constantly opened to the oil groove regardless of the rotational angle of the crank journal 54, and accordingly the lubricating oil supplied by the oil pump can constantly supplied to the slidingly contacting surface 63 of the connecting rod bearing 62 with the crank pin 61. However, when the oil groove is provided partially in the crank journal bearing 67, an end portion of the lubricating oil supplying passage is not always opened to the oil groove depending on a certain rotational angle.
In this case, since the connecting rod 57 is a member for transmitting the vertical movement of the piston 59 to the crank journal 54 through the crank pin 61, and if consideration is given to the magnitude of the combustion load acting on the coupled portion between the big and 60 and the crank pin 61, it is desirable to constantly supply the lubricating oil in-between the connecting rod bearing 62 and the crank pin 61 for lubrication.